Question

我有两张表raw_materials和raw_materials_moves。

raw_materials有字段

id, name

raw_materials_moves有此字段

id, raw_material_id, price, created

所以，我需要select每个原材料的最后3个动作

我有这个查询但不起作用

SELECT a.*, b.price, b.created
FROM raw_materials a
LEFT JOIN
 (SELECT price, raw_material_id, created FROM raw_material_moves ORDER BY created DESC LIMIT 3) b
    ON b.raw_material_id=a.id
ORDER BY a.id

Answer 1

我主要同意@chetan对变量的使用来完成这项工作。

Here is one of the best articles我在这个问题上遇到了不同的处理方式......从简单到难以理解。

Answer 2

我建议您使用DESC（或）以相反的顺序提取用户光标

Answer 3

  SELECT r1.id,name,raw_material_id 

FROM raw_materials r1, raw_materials_move r2

 WHERE r1.id=r2.id ORDER BY DESC LIMIT 3;

Answer 4

最后3个按每个原材料的创建（我假设日期）移动

select * from 
  (select a.id,a.price,a.created, 
          if(@mat=a.raw_material_id,@num:=@num+1,@num:=1) rank,
          @mat:=a.raw_material_id
     from raw_materials_moves a, (select @num:=0) b   
     order by a.raw_material_id,a.created desc) temp
where rank <=3;

请参阅demo here

Answer 5

对其进行反向排序（即... SORT BY somefield DESC），然后获得前3个（通过附加LIMIT 3）

选择每个项目的最后3行

5 个答案: